1. Field of the Invention
This invention relates generally to vehicle signal lights, and more particularly to vehicle signal lights that perform several different signaling functions.
2. Description of Related Art
Railway (i.e. railroad) transportation is popular the world over. In general, a railway includes one or more parallel series of iron or steel rails spaced apart from on another to form tracks for wheels of railway vehicles. Types of railway vehicles include locomotives, carriages, wagons, rail cars, rail motors, light rail vehicles, rail inspection vehicles, and trolleys. Reported benefits of railway transportation over motor vehicle transportation include reduced fuel consumption, improved air quality, reduced transportation costs, reduced traffic congestion, reduced pavement damage, and improved transportation safety.
As cities grow, motor vehicle traffic volumes in and around the cities typically increase. Growing cities often face the problem of accommodating this increased demand at some point. Light rail is one option that promises to reduce motor vehicle traffic congestion. In general, the term “light rail” is used to describe passenger railway vehicles operating singly or in short (e.g., two car) trains on fixed rails. The rails are typically located near motor vehicle roadways. Light rail vehicles are typically driven electrically with electrical power being drawn from an overhead electric line via a trolley or a pantograph. Light rail vehicles are also often called “streetcars,” “tramways,” or “trolley cars.”
As light rail vehicles typically operate near motor vehicles, they often include electrical signal lights similar to those used on motor vehicles. Such signal lights include brake lights, tail lights, turn signals, and running lights.
A light-emitting diode (LED) is a diode that emits light when a current passes through it. A diode is a semiconductor device through which current can pass in only one direction. LEDs are often used as indicator lights, and are also commonly used in computer system “laser” printers and compact disk read only memory (CD-ROM) drives.
LEDs are in general more efficient, last longer, and are more durable than incandescent light bulbs. LEDs are typically at least 4 times more efficient at generating light than incandescent light bulbs. Unlike incandescent light bulbs, LEDs are extremely shock resistant. While an incandescent light bulb may produce light for 1,000 operating hours, many LEDs can provide 100,000 hours of continuous use. As a result, LEDs are generally preferred over incandescent light bulbs in critical applications.
The specifications for U.S. motor vehicle signal lights are written by the Society of Automotive Engineers (SAE). These specifications are published in SAE publication HS-34 titled SAE Ground Vehicle Lighting Standards Manual, which is updated annually. The SAE standards for passenger car signal lights include:    SAE J585 “Tail Lamps (Rear Position Lamps) For Use on Motor Vehicles Less Than 2032 mm in Overall Width;”    SAE J586 “Stop Lamps for Use on Motor Vehicles Less Than 2032 mm in Overall Width;”    SAE J588 “Turn Signal Lamps for Use on Motor Vehicles Less Than 2032 mm in Overall Width;” and    SAE J1957 “Center High Mounted Stop Lamp Standard for Vehicles Less Than 2032 mm in Overall Width.”
The additional brake light required by the SAE J1957 standard is commonly referred to as the “third brake light.” Many automobile manufacturers are now using LEDs in the third brake light as the fixtures are often inaccessible making lamp replacement extremely difficult.